Chesterfield lost 2-1 to Millwall at the Proact, with manager Danny Wilson blaming the defeat on his side's defensive mistakes.
Captain Sam Morsy had given the Spireites a first half lead with a fine long ranger, but Millwall soon pegged the hosts back with an Aiden O'Brien header and soon after the break Lee Gregory netted to secure a Lions win.
Talking to PlayerHD after the game Wilson felt his side should have come away with some sort of result after some long and promising spells of football.
He said: "Up to half time we played very well, the first effort they had on goal they scored from and it's just poor defending. The second goal was the same and you can't legislate for those slip ups.
"As well as we've played we've come away with nothing and that's really not acceptable at this moment in time.
"When a game takes the pattern that it did today we should be coming away with something out of the game, it shows our Achilles heel a bit and that's disappointing."
While there were plenty of positives in the home side's performance, the boss says his side will be working on their defence in the next fortnight before Peterborough United visit the Proact in the Spireites' next game.
"We have to focus on the negative parts of the game and the defensive work needs to be looked at even more. It's not as though we don't do it on a regular basis because we do.
"We'll get back on the training ground. There's a long way to go but this is disappointing because we should have taken at least a point out of the game."
Wilson did have to deal with the late loss of Ollie Banks and Chris Herd, who both failed late fitness tests.
He explained: "Ollie had a bit of a groin problem and Chris Herd had a back spasm which is a bit unusual - both of them being ruled out before the game was a bit of a blow."